1. Field
Example embodiments of the present invention generally relate to a sheet conveying device effectively conveying various types of sheets, an image forming apparatus such as a copier, a facsimile machine, a printer, a printing machine, an inkjet recording device, a scanner provided with the sheet conveying device, and a multifunctional machine combining functions of at least two of the above.
2. Discussion of the Related Art
In order to reduce the overall sizes of related-art image forming apparatuses including copiers such as a PPC (plain paper copier) and an electrophotographic copier, facsimile machines, printers, printing machines, and inkjet recording devices, the sizes of conveying units provided therein also tend to be reduced.
Specifically, a conveying unit is used for conveying a recording medium or a sheet-type recording medium onto which an image is formed (hereinafter, referred to as “sheet”). The sheet is fed from a sheet storing unit or a sheet stacking unit in which sheets are stacked and is conveyed to a main body of an image forming apparatus. In the following description, example operations of the sheet storing unit are described.
Furthermore, the related-art image forming apparatuses generally accommodate various sheet sizes and sheet types. For example, sheets of different sizes and different types are previously stored in multiple sheet storage units. A sheet is fed from the sheet storage unit selected by a user or automatically selected by the image forming apparatus. In such a configuration, each sheet storage unit occupies a large space in the related-art image forming apparatus, and therefore, it is particularly necessary to reduce the size of the related-art conveying unit.
One approach is to have a conveying path between the sheet storage unit and a main body of the related-art image forming apparatus that considerably bends or changes its direction midway depending on the relative positions of the sheet storage unit and the main body, so as to reduce the space occupied by the conveying path. Thus, in order to change the conveying direction in a continuous and smooth manner in the conveying path, the conveying path is provided with a curved section. The curved section is given a relatively small curvature radius so that a regular-sized recording sheet normally used in the related-art image forming apparatus can be conveyed.
In one technique (a first technique) used in a sheet feeding device of a related-art image forming apparatus, sheet feed trays serving as sheet storage units are arranged beneath the main body of the image forming apparatus. Given numbers of sheets of given sheet sizes and sheet types are stacked in the sheet feed trays. In between the sheet feed trays and the main body of the related-art image forming apparatus, a sheet conveying unit is provided for extracting a sheet of paper in a substantially horizontal direction from the selected sheet feed tray and feeding the extracted sheet in an upward direction toward the main body of the image forming apparatus disposed above.
A sheet in a sheet feed tray is separated from the stack of sheets by a related-art FRR (Feed Reverse Roller) separating method, and is sent to a main body of an image forming unit through a conveying path provided with a curved section including an upper guide plate and a lower guide plate, each of which serves as a guiding member for fixing a curved section. As the sheet is conveyed further on, the sheet is pressed from above by the upper guide plate. The sheet is conveyed by an elastically deformable guide piece positioned at the outlet end of the lower guide plate and reaches a pair of conveying rollers. Hereinafter, the upper guide plate and the lower guide plate are referred to as the “guiding member for fixing a curved section.”
However, in the sheet conveying device with the above-described configuration, the following problem arises when conveying a specific type of sheet with high rigidity, such as a cardboard recording paper or an envelope. That is, when the sheet bends and moves along the curve, such a highly rigid recording paper or special paper receives a much greater resistance compared to a regular sheet such as a plain paper used for copying. This is because the curved section in the conveying path has a small radius. As a result, the highly rigid sheet cannot move along the conveying path, causing a paper jam or a conveyance failure. Thus, the sheet feeding operation cannot be reliably performed.
In order to facilitate the understanding of the related art and its problems, a description is now given of further details of the above-described conveyance operation.
When the leading edge of the sheet in the sheet conveying direction reaches the guiding member for fixing a curved section configured with the upper guide plate and the lower guide plate, the front half of the sheet including the leading edge of the sheet curves or bends in its thickness direction. Accordingly, when a highly rigid sheet is conveyed, a large force resists this bending action, in such a manner that a large resistance obstructs the sheet conveying operation. As a result, the leading edge of the highly rigid sheet may not reach the pair of conveying rollers at the downstream side of the sheet conveying direction, with the result that the sheet may be conveyed only by a pair of rollers on the upstream side thereof. However, when the sheet is bent by the guiding member, the conveying force of the pair of rollers alone may be insufficient for conveying the highly rigid sheet to counter to the resistance caused by the bending action. As a result, the following conveyance failures may be caused: Specifically, the sheet is caused to move in an oblique manner because the center-line of the highly rigid sheet does not match the center-line of the conveying path, or a paper jam occurs because the highly rigid sheet is caught inside the guiding member and stops moving.
Accordingly, the above-described sheet feeding device with the first technique has been proposed. In the sheet feeding device, a sheet is sent out from a first conveying member then conveyed to a second conveying member dos@psed at a position downstream in the conveying direction and substantially vertically above the first conveying member. A pair of linear guiding members is provided between the first conveying member and the second conveying member, and the sheet is conveyed by being guided by these linear guiding members. In this sheet feeding device, the guiding members do not have curved shapes but have linear shapes, and therefore, the conveyance load can be maintained at a low level. That is, the load can be prevented from rising abruptly so that conveyance failures such as a paper jam or oblique movements can be prevented.
That is, according to the above-described sheet feeding device, the conveyed sheet is not deformed or bent only at one position, but is deformed at two positions, i.e., near the front and the back ends of the linear guiding members in the sheet conveying direction. Furthermore, the linear guiding members are disposed obliquely at substantially intermediate angles, so that the sheet may bend by the same amount at the above-described two positions. Therefore, the conveyance load is prevented from rising abruptly. Specifically, the sheet changes its traveling direction by bending at the two positions, namely, when the sheet is passed from the pair of rollers located at the upstream side of the traveling direction to the linear guiding member, and when the sheet is passed from the linear guiding member to the pair of rollers located at the downstream side of the traveling direction. Thus, the sheet bends by smaller extents at these two positions than when the sheet abruptly bends at one position only. Thus, the resistance caused by the bending action of the sheet can be reduced at each of the two positions, thereby preventing the conveyance load from rising abruptly.
Another type of sheet feeding device with a first conveying member and a second conveying member having substantially the same configurations as the above-described sheet feeding device employing the first technique is described as follows.
This sheet feeding device employing another technique (or a second technique) includes a reverse guiding member provided at an incline between the first conveying member and the second conveying member. This reverse guiding member is configured to move toward the second conveying member.
In this sheet feeding device, when the trailing edge of the sheet contacts the reverse guiding member, the reverse guiding member shifts its position in a direction substantially according to the trailing edge of the sheet. This shift makes it possible to absorb the shock or impact caused when the trailing edge of the sheet contacts the reverse guiding member. Hence, a flipping noise can be reduced.
Yet another type of sheet feeding device with a technique (or a third technique) different from the first and second techniques has been proposed. This sheet feeding device employing the third technique includes multiple sheet storage units for storing sheets, and each of the sheet storage units is provided with a conveying path and a sheet conveying unit. The ends of the conveying paths merge into a common conveying path. Each of the conveying paths has a curved section at the end thereof, at which each conveying path merges with the common conveying path. At least one of the conveying paths provided for a sheet storage unit that stores or accommodates highly rigid sheets has a first curved section with a larger curvature radius than those of the other conveying paths.
Therefore, in this sheet feeding device, highly rigid sheets are caused to bend more moderately compared to plain paper sheets. A highly rigid sheet moves along the conveying path and passes via the first curved section having a large curvature radius, so that the sheet may not bend as much as a plain paper sheet passing via a curved section having a smaller curvature radius. Accordingly, it is possible to reduce the resistance while conveying a highly rigid sheet, so that the sheet can be conveyed to the common conveying path without being suspended or stopped.
Now, a sheet reversing unit employing another technique is described. The sheet reversing unit is provided in a related-art image forming apparatus. This sheet reversing unit includes a pair of reverse rollers and a reverse conveying path for conveying and guiding a sheet received from the pair of reverse rollers. The reverse conveying path includes a redirection section for changing the direction of conveying a sheet. Rotatable members or rollers are arranged inside the redirection section in a direction orthogonal or perpendicular to the sheet conveying direction, so that a sheet sent into the reverse conveying path can be sent out while abutting the rollers.
According to this sheet reversing unit, when a sheet is sent inside, it is ensured that the portion of the sheet inside the redirection section contacts the rollers, and the rollers are caused to rotate by or following the movement of the sheet in the conveying direction. Thus, compared to a related-art guiding plate, the conveying resistance can be reduced. Specifically, it is possible to eliminate a frictional resistance occurring between a fixed guiding member and the moving sheet while changing the conveying direction of the sheet at the redirection section.
However, the sheet conveying device of the sheet feeding device using the first technique merely provides a fixed member for guiding a conveyed sheet, and thus does not eliminate the speed difference between the conveyed sheet, which is moving, and the fixed guiding member. Accordingly, regardless of the shape or position of the guiding member, resistance occurs in such a direction as to obstruct the sheet from being conveyed, which generating a conveyance load.
That is, this related-art configuration is insufficient for preventing conveyance failures or paper jams. Although the linear guiding member can reduce the conveyance load from rising abruptly, a conveyance load is generated nonetheless. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises made by the trailing edge of the sheet increase considerably.
Furthermore, as described in reference to the sheet feeding device with the second technique, the reverse guiding member can shift its position in a direction according to the trailing edge of the sheet contacting the reverse guiding member. However, the reverse guiding member merely functions as a fixed guiding member in terms of changing the direction of the sheet. Accordingly, as with the related-art configuration described above, this related-art technique does not eliminate the relative speed difference between the sheet and the reverse guiding member when changing the direction of the sheet and guiding the sheet, thus generating a conveyance load. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises caused by the trailing edge of the sheet increase considerably.
Furthermore, as described in reference to the sheet feeding device with the third technique, the conveying path with a large curvature radius dedicated to highly rigid sheets makes it possible for sheets traveling therethrough to bend moderately so as to reduce the conveyance resistance applied by the conveying path to the sheet. However, a conveyance load is still generated nonetheless, and therefore, particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur.
Furthermore, as described in reference to the sheet reversing unit with the fourth technique, movable members such as rollers are provided at given positions inside the redirection section of the conveying path. Therefore, in the process of conveying the sheet, the frictional resistance between the sheet and the guiding member can be effectively reduced while the internal rollers are supporting the middle portion of the sheet between the leading edge and the trailing edge. However, there are no measures provided for reducing the conveyance load before and after the sheet is supported by the internal rollers, i.e., when the sheet is in contact with the conveying path outside the redirection section. Furthermore, no particular mention is made of movements of the leading edge and the trailing edge of the sheet while being conveyed. Particularly when conveying a highly rigid sheet such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises caused by the trailing edge of the sheet increase considerably.
In light of the foregoing, the inventors of the present invention previously propose to provide a sheet conveying device and an image forming apparatus including a sheet conveying device that can eliminate the drawbacks of the above-described techniques, specifically, by providing a sheet conveying device that is compact and space-saving, that includes a simple configuration achieved at low cost, and that can handle various types of sheets, and an image forming apparatus that includes such sheet conveying device.
However, the inventors of the present invention have found it difficult in practice to use the technique of this previously provided invention as is.
Specifically, the related-art separating method causes a sheet to be separated from a stack of sheets, turned at a conveying path provided with a curved section immediately after the separation, and conveyed to a grip roller. The above-described method can provide a space-saving structure having a shorter interval between the separation section and the grip roller, and at low cost.
By contrast, when a highly rigid sheet is conveyed, the sheet and a guide member of the conveying path may contact each other, thereby increasing the conveyance load.
To eliminate the above-described drawback, a belt conveying unit for supporting the conveyance of the sheet may be provided at the curved section of the conveying path. With this structure, a highly rigid sheet can be smoothly conveyed.
On the other hand, the conveying path is generally provided with a curved section having a relatively small curvature radius for providing an apparatus with a space-saving structure. In addition, when a paper jam occurs, the conveying path needs to be opened. Therefore, in most cases, the conveying path may be divided into two or more conveying paths with a branched or merged section. In a case in which a highly rigid sheet passes such a branched or merged section with a relatively small curvature radius, when the trailing edge of the highly rigid sheet moves from an upstream guide member to a downstream guide member, a sudden noise offensive to the ear or a flipping noise generated when the trailing edge of the sheet collides with or taps against the downstream guide member is produced.
The flipping noise is caused by the trailing edge of the highly rigid sheet tapping against the downstream guide member. When the trailing edge of the highly rigid sheet passes a gap provided between the upstream guide member and the downstream guide member, the trailing edge of the sheet may be released from a restrictive force of the upstream guide member and tap against the downstream guide member. This phenomenon can be eliminated when the related-art conveying roller is replaced by a moving unit with a belt.
However, to reduce the above-described flipping noise with the moving unit, it is necessary to adjust a height of the belt protruding from a conveying guide member so as to obtain reliable performance for sheets of various thicknesses.